Exogenous NAD(+) decreases oxidative stress and protects H2O2-treated RPE cells against necrotic death through the up-regulation of autophagy

Inhibition of NLRP3 inflammasome by MCC950 under hypoxia alleviates photoreceptor apoptosis via inducing autophagy in Müller glia

NLRP3 inflammasome activation has emerged as a critical initiator of inflammatory response in ischemic retinopathy. Here, we identified the effect of a potent, selective NLRP3 inhibitor, MCC950, on autophagy and apoptosis under hypoxia. Neonatal mice were exposed to hyperoxia for 5 days to establish oxygen-induced retinopathy (OIR) model. Intravitreal injection of MCC950 was given, and then autophagy and apoptosis markers were assessed. Retinal autophagy, apoptosis, and related pathways were evaluated by western blot, immunofluorescent labeling, transmission electron microscopy, and TUNEL assay. Autophagic activity in Müller glia after NLRP3 inflammasome inhibition, together with its influence on photoreceptor death, was studied using western blot, immunofluorescence staining, mRFP-GFP-LC3 adenovirus transfection, cell viability, proliferation, and apoptosis assays. Results showed that activation of NLRP3 inflammasome in Müller glia was detected in OIR model. MCC950 could improve impaired retinal autophagic flux and attenuate retinal apoptosis while it regulated the retinal AMPK/mTOR/ULK-1 pathway. Suppressed autophagy and depressed proliferation capacity resulting from hypoxia was promoted after MCC950 treatment in Müller glia. Inhibition of AMPK and ULK-1 pathway significantly interfered with the MCC950-induced autophagy activity, indicating MCC950 positively modulated autophagy through AMPK/mTOR/ULK-1 pathway in Müller cells. Furthermore, blockage of autophagy in Müller glia significantly induced apoptosis in the cocultured 661W photoreceptor cells, whereas MCC950 markedly preserved the density of photoreceptor cells. These findings substantiated the therapeutic potential of MCC950 against impaired autophagy and subsequent apoptosis under hypoxia. Such protective effect might involve the modulation of AMPK/mTOR/ULK-1 pathway. Targeting NLRP3 inflammasome in Müller glia could be beneficial for photoreceptor survival under hypoxic conditions.

Classical and Innovative Evidence for Therapeutic Strategies in Retinal Dysfunctions

The human retina is a complex anatomical structure that has no regenerative capacity. The pathogenesis of most retinopathies can be attributed to inflammation, with the activation of the inflammasome protein platform, and to the impact of oxidative stress on the regulation of apoptosis and autophagy/mitophagy in retinal cells. In recent years, new therapeutic approaches to treat retinopathies have been investigated. Experimental data suggest that the secretome of mesenchymal cells could reduce oxidative stress, autophagy, and the apoptosis of retinal cells, and in turn, the secretome of the latter could induce changes in mesenchymal cells. Other studies have evidenced that noncoding (nc)RNAs might be new targets for retinopathy treatment and novel disease biomarkers since a correlation has been found between ncRNA levels and retinopathies. A new field to explore is the interaction observed between the ocular and intestinal microbiota; indeed, recent findings have shown that the alteration of gut microbiota seems to be linked to ocular diseases, suggesting a gut-eye axis. To explore new therapeutical strategies for retinopathies, it is important to use proper models that can mimic the complexity of the retina. In this context, retinal organoids represent a good model for the study of the pathophysiology of the retina.

Construction of an Exudative Age-Related Macular Degeneration Diagnostic and Therapeutic Molecular Network Using Multi-Layer Network Analysis, a Fuzzy Logic Model, and Deep Learning Techniques: Are Retinal and Brain Neurodegenerative Disorders Related?

Neovascular age-related macular degeneration (nAMD) is a leading cause of irreversible visual impairment in the elderly. The current management of nAMD is limited and involves regular intravitreal administration of anti-vascular endothelial growth factor (anti-VEGF). However, the effectiveness of these treatments is limited by overlapping and compensatory pathways leading to unresponsiveness to anti-VEGF treatments in a significant portion of nAMD patients. Therefore, a system view of pathways involved in pathophysiology of nAMD will have significant clinical value. The aim of this study was to identify proteins, miRNAs, long non-coding RNAs (lncRNAs), various metabolites, and single-nucleotide polymorphisms (SNPs) with a significant role in the pathogenesis of nAMD. To accomplish this goal, we conducted a multi-layer network analysis, which identified 30 key genes, six miRNAs, and four lncRNAs. We also found three key metabolites that are common with AMD, Alzheimer's disease (AD) and schizophrenia. Moreover, we identified nine key SNPs and their related genes that are common among AMD, AD, schizophrenia, multiple sclerosis (MS), and Parkinson's disease (PD). Thus, our findings suggest that there exists a connection between nAMD and the aforementioned neurodegenerative disorders. In addition, our study also demonstrates the effectiveness of using artificial intelligence, specifically the LSTM network, a fuzzy logic model, and genetic algorithms, to identify important metabolites in complex metabolic pathways to open new avenues for the design and/or repurposing of drugs for nAMD treatment.

NAD+ metabolism and eye diseases: current status and future directions

Currently, there are no truly effective treatments for a variety of eye diseases, such as glaucoma, age-related macular degeneration (AMD), and inherited retinal degenerations (IRDs). These conditions have a significant impact on patients' quality of life and can be a burden on society. However, these diseases share a common pathological process of NAD+ metabolism disorders. They are either associated with genetically induced primary NAD+ synthase deficiency, decreased NAD+ levels due to aging, or enhanced NAD+ consuming enzyme activity during disease pathology. In this discussion, we explore the role of NAD+ metabolic disorders in the development of associated ocular diseases and the potential advantages and disadvantages of various methods to increase NAD+ levels. It is essential to carefully evaluate the possible adverse effects of these methods and conduct a more comprehensive and objective assessment of their function before considering their use.

Stages, pathogenesis, clinical management and advancements in therapies of age-related macular degeneration

Age-related macular degeneration (AMD) is a retinal degenerative disorder prevalent in the elderly population, which leads to the loss of central vision. The disease progression can be managed, if not prevented, either by blocking neovascularization ("wet" form of AMD) or by preserving retinal pigment epithelium and photoreceptor cells ("dry" form of AMD). Although current therapeutic modalities are moderately successful in delaying the progression and management of the disease, advances over the past years in regenerative medicine using iPSC, embryonic stem cells, advanced materials (including nanomaterials) and organ bio-printing show great prospects in restoring vision and efficient management of either forms of AMD. This review focuses on the molecular mechanism of the disease, model systems (both cellular and animal) used in studying AMD, the list of various regenerative therapies and the current treatments available. The article also highlights on the recent clinical trials using regenerative therapies and management of the disease.

Developmental changes in cerebral NAD and neuroenergetics of an antioxidant compromised mouse model of schizophrenia

Defects in essential metabolic regulation for energy supply, increased oxidative stress promoting excitatory/inhibitory imbalance and phospholipid membrane dysfunction have been implicated in the pathophysiology of schizophrenia (SZ). The knowledge about the developmental trajectory of these key pathophysiological components and their interplay is important to develop new preventive and treatment strategies. However, this assertion is so far limited. To investigate the developmental regulations of these key components in the brain, we assessed, for the first time, in vivo redox state from the oxidized (NAD+) and reduced (NADH) form of Nicotinamide Adenine Dinucleotide (NAD), energy and membrane metabolites, inhibitory and excitatory neurotransmitters by 31P and 1H MRS during the neurodevelopment of an SZ animal model with genetically compromised glutathione synthesis (gclm-KO mice). When compared to age-matched wild type (WT), an increase in NAD+/NADH redox ratio was found in gclm-KO mice until early adulthood, followed by a decrease in full adults as observed in patients. Especially, in early postnatal life (P20, corresponding to childhood), levels of several metabolites were altered in gclm-KO mice, including NAD+, NAD+/NADH, ATP, and glutamine + glutamate, suggesting an interactive compensation for redox dysregulation between NAD, energy metabolism, and neurotransmission. The identified temporal neurometabolic regulations under deficits in redox regulation provide insights into preventive treatment targets for at-risk individuals, and other neurodevelopmental disorders involving oxidative stress and energetic dysfunction.

Hydrogen peroxide-induced oxidative damage and protective role of peroxiredoxin 6 protein via EGFR/ERK signaling pathway in RPE cells

Introduction

Damage to retinal pigment epithelium (RPE) cells caused by oxidative stress is closely related to the pathogenesis of several blinding retinal diseases, such as age-related macular degeneration (AMD), retinitis pigmentosa, and other inherited retinal degenerative conditions. However, the mechanisms of this process are poorly understood. Hence, the goal of this study was to investigate hydrogen peroxide (H₂O₂)-induced oxidative damage and protective role of peroxiredoxin 6 (PRDX6) protein via EGFR/ERK signaling pathway in RPE cells.

Methods

Cells from a human RPE cell line (ARPE-19 cells) were treated with H₂O₂, and then cell viability was assessed using the methyl thiazolyl tetrazolium assay. Cell death and reactive oxygen species (ROS) were detected by flow cytometry. The levels of PRDX6, epidermal growth factor receptor (EGFR), P38 mitogen-activated protein kinase (P38MAPK), c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) were detected by Western blot assay. PRDX6 and EGFR were also detected via immunofluorescence staining.

Results

Our results show that H₂O₂ inhibited cell viability, induced cell death, and increased ROS levels in ARPE-19 cells. It was also found that H₂O₂ decreased the levels of PRDX6, EGFR, and phosphorylated ERK but increased the levels of phosphorylated P38MAPK and JNK. PRDX6 overexpression was found to attenuate H₂O₂-induced inhibition of cell viability and increased cell death and ROS production in ARPE-19 cells. PRDX6 overexpression also increased the expression of EGFR and alleviated the H₂O₂-induced decrease in EGFR and phosphorylated ERK. Moreover, inhibition of epidermal growth factor-induced EGFR and ERK signaling in oxidative stress was partially blocked by PRDX6 overexpression.

Discussion

Our findings indicate that PRDX6 overexpression protects RPE cells from oxidative stress damage caused by decreasing ROS production and partially blocking the inhibition of the EGFR/ERK signaling pathway induced by oxidative stress. Therefore, PRDX6 shows promise as a therapeutic target for the prevention of RPE cell damage caused by oxidative stress associated with retinal diseases.

Proteomic analysis reveals microvesicles containing NAMPT as mediators of radioresistance in glioma

Tumor-initiating cells contained within the aggressive brain tumor glioma (glioma stem cells, GSCs) promote radioresistance and disease recurrence. However, mechanisms of resistance are not well understood. Herein, we show that the proteome-level regulation occurring upon radiation treatment of several patient-derived GSC lines predicts their resistance status, whereas glioma transcriptional subtypes do not. We identify a mechanism of radioresistance mediated by the transfer of the metabolic enzyme NAMPT to radiosensitive cells through microvesicles (NAMPT-high MVs) shed by resistant GSCs. NAMPT-high MVs rescue the proliferation of radiosensitive GSCs and fibroblasts upon irradiation, and upon treatment with a radiomimetic drug or low serum, and increase intracellular NAD(H) levels. Finally, we show that the presence of NAMPT within the MVs and its enzymatic activity in recipient cells are necessary to mediate these effects. Collectively, we demonstrate that the proteome of GSCs provides unique information as it predicts the ability of glioma to resist radiation treatment. Furthermore, we establish NAMPT transfer via MVs as a mechanism for rescuing the proliferation of radiosensitive cells upon irradiation.

Innate immunity dysregulation in aging eye and therapeutic interventions

The prevalence of eye diseases increases considerably with age, resulting in significant vision impairment. Although the pathobiology of age-related eye diseases has been studied extensively, the contribution of immune-related changes due to aging remains elusive. In the eye, tissue-resident cells and infiltrating immune cells regulate innate responses during injury or infection. But due to aging, these cells lose their protective functions and acquire pathological phenotypes. Thus, dysregulated ocular innate immunity in the elderly increases the susceptibility and severity of eye diseases. Herein, we emphasize the impact of aging on the ocular innate immune system in the pathogenesis of infectious and non-infectious eye diseases. We discuss the role of age-related alterations in cellular metabolism, epigenetics, and cellular senescence as mechanisms underlying altered innate immune functions. Finally, we describe approaches to restore protective innate immune functions in the aging eye. Overall, the review summarizes our current understanding of innate immune functions in eye diseases and their dysregulation during aging.

Mitochondrial activity is the key to the protective effect of β-Lapachone, a NAD+ booster, in healthy cells against cisplatin cytotoxicity

BACKGROUND

Cisplatin (CDDP) is a first-line chemotherapeutic drug for treating various cancers. However, CDDP also damages normal cells and causes many side effects. Recently, CDDP has been demonstrated to kill cancer cells by targeting mitochondria. Protecting mitochondria might be a potential therapeutic strategy for CDDP-induced side effects. β-Lapachone (β-lap), a recognized NAD⁺ booster, has been reported to regulate mitochondrial activity. However, it remains unclear whether maintaining mitochondrial activity is the key factor in the protective effects of β-lap in CDDP-treated normal cells.

PURPOSE

In this study, the protective effects of β-lap on mitochondria against CDDP cytotoxicity in normal cells were evaluated.

STUDY DESIGN

In vitro cell models were used in this study, including 3T3 fibroblasts, human dermal fibroblasts, MCF-7 breast cancer cells, and MDA-MB-231 breast cancer cells.

METHODS

Cells were treated with CDDP and β-lap, and cell survival, NAD⁺, mitochondrial activity, autophagy, and ATP production were measured. Various inhibitors and siRNAs were used to confirm the key signal underlying the protective effects of β-lap.

RESULTS

The results demonstrated that β-lap significantly decreased CDDP cytotoxicity in normal fibroblasts. With various inhibitors and siRNAs, β-lap reduced CDDP-induced damage to normal fibroblasts by maintaining mitochondrial activity and increasing autophagy through the NQO1/NAD⁺/SIRT1 axis. Most importantly, the protective effects of β-lap in fibroblasts did not affect the therapeutic effects of CDDP in cancer cells. This study indicated that mitochondrial activity, energy production, and NQO1 levels might be crucial responses separating normal cells from cancer cells under exposure to CDDP and β-lap.

CONCLUSION

β-lap could be a good synergistic drug for reducing the side effects of CDDP without affecting the anticancer drug effect.

Metabolic Imbalance Effect on Retinal Müller Glial Cells Reprogramming Capacity: Involvement of Histone Deacetylase SIRT6

Retinal Müller glial cells (MGs) are among the first to demonstrate metabolic changes during retinal disease and are a potential source of regenerative cells. In response to a harmful stimulus, they can dedifferentiate acquiring neural stem cells properties, proliferate and migrate to the damaged retinal layer and differentiate into lost neurons. However, it is not yet known how this reprogramming process is regulated in mammals. Since glucose and oxygen are important regulatory elements that may help directing stem cell fate, we aimed to study the effect of glucose variations and oxidative stress in Müller cells reprogramming capacity and analyze the participation the histone deacetylase SIRT6, as an epigenetic modulator of this process. We found that the combination of high glucose and oxidative stress induced a decrease in the levels of the marker glutamine synthetase, and an increase in the migration capacity of the cells suggesting that these experimental conditions could induce some degree of dedifferentiation and favor the migration ability. High glucose induced an increase in the levels of the pluripotent factor SOX9 and a decrease in SIRT6 levels accompanied by the increase in the acetylation levels of H3K9. Inhibiting SIRT6 expression by siRNA rendered an increase in SOX9 levels. We also determined SOX9 levels in retinas from mice with a conditional deletion of SIRT6 in the CNS. To further understand the mechanisms that regulate MGs response under metabolic impaired conditions, we evaluated the gene expression profile and performed Gene Ontology enrichment analysis of Müller cells from a murine model of Diabetes. We found several differentially expressed genes and observed that the transcriptomic change involved the enrichment of genes associated with glucose metabolism, cell migration, development and pluripotency. We found that many functional categories affected in cells of diabetic animals were directly related to SIRT6 function. Transcription factors enrichment analysis allowed us to predict several factors, including SOX9, that may be involved in the modulation of the differential expression program observed in diabetic MGs. Our results underline the heterogeneity of Müller cells response and the challenge that the study of metabolic impairment in vivo represents.

An In-Silico, In-Vitro and In-Vivo Combined Approach to Identify NMNATs as Potential Protein Targets of ProEGCG for Treatment of Endometriosis

Endometriosis is defined as endometrial tissues found outside the uterine cavity. ProEGCG is a prodrug of Epigallocatechin gallate (EGCG), a potent polyphenol found in green tea. It inhibits the development of endometriotic lesions of mouse model in vivo, with higher efficacy and more remarkable anti-oxidative ability than EGCG. Our study aims to identify the molecular binding targets and pharmacological actions of ProEGCG in treating endometriosis. Protein target interaction study is essential to fully characterize the mechanism of actions, related therapeutic effects, and side effects. We employed a combined approach, starting with an in silico reverse screening of protein targets and molecular docking, followed by in vitro cellular thermal shift assay (CESTA) to assess the stability of protein-small molecule complexes. Then microarray and immunostaining of endometriotic lesions in mice in vivo confirmed the molecular interaction of the selected targets after treatment. Our study identified enzymes nicotinamide nucleotide adenylyltransferase (NMNAT)1 and NMNAT3 as protein targets of ProEGCG in silico and in vitro and were overexpressed after ProEGCG treatment in vivo. These findings suggested that participation in nicotinate and nicotinamide metabolism potentially regulated the redox status of endometriosis via its antioxidative capacities through binding to the potential therapeutic targets of ProEGCG.

Codonopsis pilosula Polysaccharides Alleviate Aβ 1-40-Induced PC12 Cells Energy Dysmetabolism via CD38/NAD+ Signaling Pathway

Background

Alzheimer's disease (AD) is the most common type of dementia and has a complex pathogenesis with no effective treatment. Energy metabolism disorders, as an early pathological event of AD,have attracted attention as a promising area of AD research. Codonopsis pilosula Polysaccharides are the main effective components of Codonopsis pilosula, which have been demonstrated to regulate energy metabolism.

Methods

In order to further study the roles and mechanisms of Codonopsis pilosula polysaccharides in AD, this study used an Aβ_1-40-induced PC12 cells model to study the protective effects of Codonopsis pilosula polysaccharides and their potential mechanisms in improving energy metabolism dysfunction.

Results

The results showed that Aβ_1-40 induced a decrease in PC12 cells viability, energy metabolism molecules (ATP, NAD+, and NAD+/NADH) and Mitochondrial Membrane Potential (MMP) and an increase in ROS. Additionally, it was found that Aβ_1-40 increased CD38 expression related to NAD+ homeostasis, whereas Silent Information Regulation 2 homolog1 (SIRT1, SIRT3), Peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) and SIRT3 activity were decreased. Codonopsis pilosula polysaccharides increased NAD+, NAD+/NADH, SIRT3, SIRT1, and PGC-1α related to NAD+, thus partially recovering ATP.

Conclusion

Our findings reveal that Codonopsis pilosula polysaccharides protected PC12 cells from Aβ_1-40-induced damage, suggesting that these components of the Codonopsis pilosula herb may represent an early treatment option for AD patients.

MERTK-Mediated LC3-Associated Phagocytosis (LAP) of Apoptotic Substrates in Blood-Separated Tissues: Retina, Testis, Ovarian Follicles

Timely and efficient elimination of apoptotic substrates, continuously produced during one’s lifespan, is a vital need for all tissues of the body. This task is achieved by cells endowed with phagocytic activity. In blood-separated tissues such as the retina, the testis and the ovaries, the resident cells of epithelial origin as retinal pigmented epithelial cells (RPE), testis Sertoli cells and ovarian granulosa cells (GC) provide phagocytic cleaning of apoptotic cells and cell membranes. Disruption of this process leads to functional ablation as blindness in the retina and compromised fertility in males and females. To ensure the efficient elimination of apoptotic substrates, RPE, Sertoli cells and GC combine various mechanisms allowing maintenance of tissue homeostasis and avoiding acute inflammation, tissue disorganization and functional ablation. In tight cooperation with other phagocytosis receptors, MERTK—a member of the TAM family of receptor tyrosine kinases (RTK)—plays a pivotal role in apoptotic substrate cleaning from the retina, the testis and the ovaries through unconventional autophagy-assisted phagocytosis process LAP (LC3-associated phagocytosis). In this review, we focus on the interplay between TAM RTKs, autophagy-related proteins, LAP, and Toll-like receptors (TLR), as well as the regulatory mechanisms allowing these components to sustain tissue homeostasis and prevent functional ablation of the retina, the testis and the ovaries.

PARP-1 activation after oxidative insult promotes energy stress-dependent phosphorylation of YAP1 and reduces cell viability

Poly(ADP-ribose) polymerase 1 (PARP-1) is a nuclear enzyme that catalyze the transfer of ADP-ribose units from NAD+ to several target proteins involved in cellular stress responses. Using WRL68 (HeLa derivate) cells, we previously showed that PARP-1 activation induced by oxidative stress after H2O2 treatment lead to depletion of cellular NAD+ and ATP, which promoted cell death. In this work, LC-MS/MS-based phosphoproteomics in WRL68 cells showed that the oxidative damage induced by H2O2 increased the phosphorylation of YAP1, a transcriptional co-activator involved in cell survival, and modified the phosphorylation of other proteins involved in transcription. Genetic or pharmacological inhibition of PARP-1 in H2O2-treated cells reduced YAP1 phosphorylation and degradation and increased cell viability. YAP1 silencing abrogated the protective effect of PARP-1 inhibition, indicating that YAP1 is important for the survival of WRL68 cells exposed to oxidative damage. Supplementation of NAD+ also reduced YAP1 phosphorylation, suggesting that the loss of cellular NAD+ caused by PARP-1 activation after oxidative treatment is responsible for the phosphorylation of YAP1. Finally, PARP-1 silencing after oxidative treatment diminished the activation of the metabolic sensor AMPK. Since NAD+ supplementation reduced the phosphorylation of some AMPK substrates, we hypothesized that the loss of cellular NAD+ after PARP-1 activation may induce an energy stress that activates AMPK. In summary, we showed a new crucial role of PARP-1 in the response to oxidative stress in which PARP-1 activation reduced cell viability by promoting the phosphorylation and degradation of YAP1 through a mechanism that involves the depletion of NAD+.

Mitophagy: An Emerging Target in Ocular Pathology

Mitochondrial function is essential for the viability of aerobic eukaryotic cells, as mitochondria provide energy through the generation of adenosine triphosphate (ATP), regulate cellular metabolism, provide redox balancing, participate in immune signaling, and can initiate apoptosis. Mitochondria are dynamic organelles that participate in a cyclical and ongoing process of regeneration and autophagy (clearance), termed mitophagy specifically for mitochondrial (macro)autophagy. An imbalance in mitochondrial function toward mitochondrial dysfunction can be catastrophic for cells and has been characterized in several common ophthalmic diseases. In this article, we review mitochondrial homeostasis in detail, focusing on the balance of mitochondrial dynamics including the processes of fission and fusion, and provide a description of the mechanisms involved in mitophagy. Furthermore, this article reviews investigations of ocular diseases with impaired mitophagy, including Fuchs endothelial corneal dystrophy, primary open-angle glaucoma, diabetic retinopathy, and age-related macular degeneration, as well as several primary mitochondrial diseases with ocular phenotypes that display impaired mitophagy, including mitochondrial encephalopathy lactic acidosis stroke, Leber hereditary optic neuropathy, and chronic progressive external ophthalmoplegia. The results of various studies using cell culture, animal, and human tissue models are presented and reflect a growing awareness of mitophagy impairment as an important feature of ophthalmic disease pathology. As this review indicates, it is imperative that mitophagy be investigated as a targetable mechanism in developing therapies for ocular diseases characterized by oxidative stress and mitochondrial dysfunction.

Improving the production of NAD+ via multi-strategy metabolic engineering in Escherichia coli

Nicotinamide adenine dinucleotide (NAD⁺) is an essential coenzyme involved in numerous physiological processes. As an attractive product in the industrial field, NAD⁺ also plays an important role in oxidoreductase-catalyzed reactions, drug synthesis, and the treatment of diseases, such as dementia, diabetes, and vascular dysfunction. Currently, although the biotechnology to construct NAD⁺-overproducing strains has been developed, limited regulation and low productivity still hamper its use on large scales. Here, we describe multi-strategy metabolic engineering to address the NAD⁺-production bottleneck in E. coli. First, blocking the degradation pathway of NAD(H) increased the accumulation of NAD⁺ by 39%. Second, key enzymes involved in the Preiss-Handler pathway of NAD⁺ synthesis were overexpressed and led to a 221% increase in the NAD⁺ concentration. Third, the PRPP synthesis module and Preiss-Handler pathway were combined to strengthen the precursors supply, which resulted in enhancement of NAD⁺ content by 520%. Fourth, increasing the ATP content led to an increase in the concentration of NAD⁺ by 170%. Finally, with the combination of all above strategies, a strain with a high yield of NAD⁺ was constructed, with the intracellular NAD⁺ concentration reaching 26.9 μmol/g DCW, which was 834% that of the parent strain. This study presents an efficient design of an NAD⁺-producing strain through global regulation metabolic engineering.

Exogenous NAD+ Postpones the D-Gal-Induced Senescence of Bone Marrow-Derived Mesenchymal Stem Cells via Sirt1 Signaling

Cell senescence is accompanied by decreased nicotinamide adenine dinucleotide (NAD⁺) levels; however, whether exogenous NAD⁺ affects bone marrow-derived mesenchymal stem cells (BMSCs) senescence and the involved mechanisms is still unclear. Here, we find that exogenous NAD⁺ replenishment significantly postpones BMSC senescence induced by D-galactose (D-gal). It is also shown that exogenous NAD⁺ leads to increased intracellular NAD⁺ levels and reduced intracellular reactive oxygen species in senescent BMSCs here. Further investigation showed that exogenous NAD⁺ weakened BMSC senescence by increasing Sirtuin 1 (Sirt1) expression. Moreover, exogenous NAD⁺ reduced senescence-associated-β-galactosidase activity, and downregulated poly (ADP-ribose) polymerase 1 expression. In addition, the reduced expression of Sirt1 by small interfering RNA abolished the beneficial effects of exogenous NAD⁺ in terms of postponing BMSCs senescence induced by D-gal. Taken together, our results indicate that exogenous NAD⁺ could postpone D-gal-induced BMSC senescence through Sirt1 signaling, providing a potential method for obtaining high quality BMSCs to support their research and clinical application.

Spermidine Attenuates Oxidative Stress-Induced Apoptosis via Blocking Ca2+ Overload in Retinal Pigment Epithelial Cells Independently of ROS

Retinal pigment epithelial (RPE) cells occupy the outer layer of the retina and perform various biological functions. Oxidative damage to RPE cells is a major risk factor for retinal degeneration that ultimately leads to vision loss. In this study, we investigated the role of spermidine in a hydrogen peroxide (H₂O₂)-induced oxidative stress model using human RPE cells. Our findings showed that 300 μM H₂O₂ increased cytotoxicity, apoptosis, and cell cycle arrest in the G2/M phase, whereas these effects were markedly suppressed by 10 μM spermidine. Furthermore, spermidine significantly reduced H₂O₂-induced mitochondrial dysfunction including mitochondrial membrane potential and mitochondrial activity. Although spermidine displays antioxidant properties, the generation of intracellular reactive oxygen species (ROS) upon H₂O₂ insult was not regulated by spermidine. Spermidine did suppress the increase in cytosolic Ca²⁺ levels resulting from endoplasmic reticulum stress in H₂O₂-stimulated human RPE cells. Treatment with a cytosolic Ca²⁺ chelator markedly reversed H₂O₂-induced cellular dysfunction. Overall, spermidine protected against H₂O₂-induced cellular damage by blocking the increase of intracellular Ca²⁺ independently of ROS. These results suggest that spermidine protects RPE cells from oxidative stress, which could be a useful treatment for retinal diseases.

Inhibition of InsP3R with Xestospongin B Reduces Mitochondrial Respiration and Induces Selective Cell Death in T Cell Acute Lymphoblastic Leukemia Cells

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy whose chemoresistance and relapse persist as a problem despite significant advances in its chemotherapeutic treatments. Mitochondrial metabolism has emerged as an interesting therapeutic target given its essential role in maintaining bioenergetic and metabolic homeostasis. T-ALL cells are characterized by high levels of mitochondrial respiration, making them suitable for this type of intervention. Mitochondrial function is sustained by a constitutive transfer of calcium from the endoplasmic reticulum to mitochondria through the inositol 1,4,5-trisphosphate receptor (InsP3R), making T-ALL cells vulnerable to its inhibition. Here, we determine the bioenergetic profile of the T-ALL cell lines CCRF-CEM and Jurkat and evaluate their sensitivity to InsP3R inhibition with the specific inhibitor, Xestospongin B (XeB). Our results show that T-ALL cell lines exhibit higher mitochondrial respiration than non-malignant cells, which is blunted by the inhibition of the InsP3R. Prolonged treatment with XeB causes T-ALL cell death without affecting the normal counterpart. Moreover, the combination of XeB and glucocorticoids significantly enhanced cell death in the CCRF-CEM cells. The inhibition of InsP3R with XeB rises as a potential therapeutic alternative for the treatment of T-ALL.

Potential Therapeutic Benefit of NAD+ Supplementation for Glaucoma and Age-Related Macular Degeneration

Glaucoma and age-related macular degeneration are leading causes of irreversible blindness worldwide with significant health and societal burdens. To date, no clinical cures are available and treatments target only the manageable symptoms and risk factors (but do not remediate the underlying pathology of the disease). Both diseases are neurodegenerative in their pathology of the retina and as such many of the events that trigger cell dysfunction, degeneration, and eventual loss are due to mitochondrial dysfunction, inflammation, and oxidative stress. Here, we critically review how a decreased bioavailability of nicotinamide adenine dinucleotide (NAD; a crucial metabolite in healthy and disease states) may underpin many of these aberrant mechanisms. We propose how exogenous sources of NAD may become a therapeutic standard for the treatment of these conditions.

Axonal Protection by Nicotinamide Riboside via SIRT1-Autophagy Pathway in TNF-Induced Optic Nerve Degeneration

Nicotinamide adenine dinucleotide (NAD⁺) synthesis pathway has been involved in many biological functions. Nicotinamide riboside (NR) is widely used as an NAD⁺ precursor and known to increase NAD⁺ level in several tissues. The present study aimed to examine the effect of NR on tumor necrosis factor (TNF)-induced optic nerve degeneration and to investigate whether it alters SIRT1 expression and autophagic status in optic nerve. We also examined the localization of nicotinamide riboside kinase 1 (NRK1), which is a downstream enzyme for NR biosynthesis pathway in retina and optic nerve. Intravitreal injection of TNF or TNF plus NR was performed on rats. The p62 and LC3-II protein levels were examined to evaluate autophagic flux in optic nerve. Immunohistochemical analysis was performed to localize NRK1 expression. Morphometric analysis showed substantial axonal protection by NR against TNF-induced axon loss. TNF-induced increment of p62 protein level was significantly inhibited by NR administration. NR administration alone significantly increased the LC3-II levels and reduced p62 levels compared with the basal levels, and upregulated SIRT1 levels in optic nerve. Immunohistochemical analysis showed that NRK1 exists in retinal ganglion cells (RGCs) and nerve fibers in retina and optic nerve. NR administration apparently upregulated NRK1 levels in the TNF-treated eyes as well as the control eyes. Pre-injection of an SIRT1 inhibitor resulted in a significant increase of p62 levels in the NR plus TNF treatment group, implicating that SIRT1 regulates autophagy status. In conclusion, NRK1 exists in RGCs and optic nerve axons. NR exerted protection against axon loss induced by TNF with possible involvement of upregulated NRK1 and SIRT1-autophagy pathway.

Influence of NAD+ as an ageing-related immunomodulator on COVID 19 infection: A hypothesis

The aging-associated decline of biological functions represents an important contributor to the increase in morbidity and mortality of human beings. Of these biological functions deterioration; there is a significant decline in the heart function, impairments in the lungs gas exchange, and impairments in the immune function. Many alterations in the body humeral and cellular immune response were observed with ageing process: The circulating pro-inflammatory cytokines are increased, the naive lymphocytes are decreased, the numbers of the antigen-presenting cells areelevated and the overall response is impaired. In addition, ageing is associated with a progressive restriction in the telomere length. Telomeres are located at chromosomes ends and play an essential role in preserving chromosome stability. Also, telomere length is very important to the immune system, because of the high sensitivity of the immune cells to the shortening of telomeres. Telomeres shortening adversely affect the immune cells' function and developments. These adverse changes increased the susceptibility for severe infection, risk of hospitalization, and even death. Elderly COVID-19 patients are at a real risk of complications due to impaired immune function, cytokine storm and defective respiratory function. Administration of anti-ageing immunomodulation factors like Nicotinamide Adenine Dinucleotide NAD+ can minimize these changes through its potent immunomodulation and longevity effects. NAD+ has a direct inhibitory effect on PARP-1 and can prevent pro-inflammatory cytokines over-activation. Increasing the NAD+ level will also result in stabilizing telomeres and this has a positive impact on immune cells function.

Implications of NAD+ Metabolism in the Aging Retina and Retinal Degeneration

Nicotinamide adenine dinucleotide (NAD⁺) plays an important role in various key biological processes including energy metabolism, DNA repair, and gene expression. Accumulating clinical and experimental evidence highlights an age-dependent decline in NAD⁺ levels and its association with the development and progression of several age-related diseases. This supports the establishment of NAD⁺ as a critical regulator of aging and longevity and, relatedly, a promising therapeutic target to counter adverse events associated with the normal process of aging and/or the development and progression of age-related disease. Relative to the above, the metabolism of NAD⁺ has been the subject of numerous investigations in various cells, tissues, and organ systems; however, interestingly, studies of NAD⁺ metabolism in the retina and its relevance to the regulation of visual health and function are comparatively few. This is surprising given the critical causative impact of mitochondrial oxidative damage and bioenergetic crises on the development and progression of degenerative disease of the retina. Hence, the role of NAD⁺ in this tissue, normally and aging and/or disease, should not be ignored. Herein, we discuss important findings in the field of NAD⁺ metabolism, with particular emphasis on the importance of the NAD⁺ biosynthesizing enzyme NAMPT, the related metabolism of NAD⁺ in the retina, and the consequences of NAMPT and NAD⁺ deficiency or depletion in this tissue in aging and disease. We discuss also the implications of potential therapeutic strategies that augment NAD⁺ levels on the preservation of retinal health and function in the above conditions. The overarching goal of this review is to emphasize the importance of NAD⁺ metabolism in normal, aging, and/or diseased retina and, by so doing, highlight the necessity of additional clinical studies dedicated to evaluating the therapeutic utility of strategies that enhance NAD⁺ levels in improving vision.

Oxyresveratrol Induces Autophagy via the ER Stress Signaling Pathway, and Oxyresveratrol-Induced Autophagy Stimulates MUC2 Synthesis in Human Goblet Cells

Background: Autophagy is a cell protection system invoked to eliminate the damaged organelles and misfolded proteins that induce various stresses, including endoplasmic reticulum (ER) stress. Autophagy can control mucin secretion in goblet cells. Oxyresveratrol (OXY), an antioxidant, stimulates expression of MUC2. Thus, we investigated the effect of OXY on autophagy and found that OXY-induced autophagy stimulates MUC2 expression in human intestinal goblet cells. Methods: Autophagy-related genes and proteins were examined by quantitative real-time PCR (qPCR) and Western blotting, respectively. Autophagy was assessed by immunocytochemistry (ICC). To analyze the protein expression profiles of OXY-treated LS 174T goblet cells, two-dimensional electrophoresis (2DE) and peptide mass fingerprinting (PMF) were performed. MUC2 expression in cells was evaluated by ICC. Results: OXY significantly increased the expression levels of genes related to autophagy induction, and activated phagosome elongation resulted in the formation of autophagosomes. OXY also activated the ER stress signaling pathway and promoted MUC2 synthesis, which was inhibited by treatment with an autophagy inhibitor. Conclusion: OXY induces autophagy via the ER stress signaling pathway, and OXY-induced autophagy increases MUC2 production in intestinal goblet cells.

Nicotinamide Increases Intracellular NAD+ Content to Enhance Autophagy-Mediated Group A Streptococcal Clearance in Endothelial Cells

Group A streptococcus (GAS) is a versatile pathogen that causes a wide spectrum of diseases in humans. Invading host cells is a known strategy for GAS to avoid antibiotic killing and immune recognition. However, the underlying mechanisms of GAS resistance to intracellular killing need to be explored. Endothelial HMEC-1 cells were infected with GAS, methicillin-resistant Staphylococcus aureus (MRSA) and Salmonella Typhimurium under nicotinamide (NAM)-supplemented conditions. The intracellular NAD⁺ level and cell viability were respectively measured by NAD⁺ quantification kit and protease-based cytotoxicity assay. Moreover, the intracellular bacteria were analyzed by colony-forming assay, transmission electron microscopy, and confocal microscopy. We found that supplementation with exogenous nicotinamide during infection significantly inhibited the growth of intracellular GAS in endothelial cells. Moreover, the NAD⁺ content and NAD⁺/NADH ratio of GAS-infected endothelial cells were dramatically increased, whereas the cell cytotoxicity was decreased by exogenous nicotinamide treatment. After knockdown of the autophagy-related ATG9A, the intracellular bacterial load was increased in nicotinamide-treated endothelial cells. The results of Western blot and transmission electron microscopy also revealed that cells treated with nicotinamide can increase autophagy-associated LC3 conversion and double-membrane formation during GAS infection. Confocal microscopy images further showed that more GAS-containing vacuoles were colocalized with lysosome under nicotinamide-supplemented conditions than without nicotinamide treatment. In contrast to GAS, supplementation with exogenous nicotinamide did not effectively inhibit the growth of MRSA or S. Typhimurium in endothelial cells. These results indicate that intracellular NAD⁺ homeostasis is crucial for controlling intracellular GAS infection in endothelial cells. In addition, nicotinamide may be a potential new therapeutic agent to overcome persistent infections of GAS.

Inhibition of NAMPT markedly enhances plasma-activated medium-induced cell death in human breast cancer MDA-MB-231 cells

Plasma-activated medium (PAM), which is prepared by non-thermal atmospheric pressure plasma (NTP) irradiation of cell-free medium, has been shown to exhibit tumor-specific cytotoxicity. Since PAM contains reactive oxygen species (ROS) and reactive nitrogen species (RNS), its anticancer effects are considered to be responsible for oxidative stress induced by these reactive molecules. We previously reported that PAM-induced cell death is closely related to energy failure associated with a decrease in intracellular nicotinamide adenine dinucleotide (NAD⁺) and ATP levels. Nicotinamide phosphoribosyltransferase (NAMPT), which is a rate-limiting enzyme for NAD⁺ synthesis in the salvage pathway, was shown to be overexpressed in many types of cancer cells. The NAMPT inhibitor FK866 significantly depletes NAD⁺ and subsequently suppresses cancer cell proliferation. In this study, we examined the effects of FK866 on PAM-induced cytotoxicity using human breast cancer MDA-MB-231 cells. FK866 dose-dependently enhanced PAM-induced cell death in MDA-MB-231 cells. The combination of PAM and FK866 markedly induced intracellular NAD⁺ and ATP depletion. Knockdown of NAMPT by siRNA increased the cytotoxicity of PAM. The addition of NAD⁺ mitigated PAM-induced cell death. In addition, cotreatment with PAM and FK866 augmented ROS production and the decrease in intracellular reduced glutathione (GSH) compared to treatment with PAM alone. FK866 had little effect on PAM-induced mitochondrial dysfunction. Furthermore, the combination of PAM and FK866 decreased the level of NADPH, which is required for GSH metabolism, compared with PAM alone. Taken together, we conclude that cotreatment with NAMPT inhibitors is beneficial for anticancer therapy using PAM.

Diverse therapeutic efficacies and more diverse mechanisms of nicotinamide

BACKGROUND

Nicotinamide (NAM) is a form of vitamin B3 that, when administered at near-gram doses, has been shown or suggested to be therapeutically effective against many diseases and conditions. The target conditions are incredibly diverse ranging from skin disorders such as bullous pemphigoid to schizophrenia and depression and even AIDS. Similar diversity is expected for the underlying mechanisms. In a large portion of the conditions, NAM conversion to nicotinamide adenine dinucleotide (NAD⁺) may be a major factor in its efficacy. The augmentation of cellular NAD⁺ level not only modulates mitochondrial production of ATP and superoxide, but also activates many enzymes. Activated sirtuin proteins, a family of NAD⁺-dependent deacetylases, play important roles in many of NAM's effects such as an increase in mitochondrial quality and cell viability countering neuronal damages and metabolic diseases. Meanwhile, certain observed effects are mediated by NAM itself. However, our understanding on the mechanisms of NAM's effects is limited to those involving certain key proteins and may even be inaccurate in some proposed cases.

AIM OF REVIEW

This review details the conditions that NAM has been shown to or is expected to effectively treat in humans and animals and evaluates the proposed underlying molecular mechanisms, with the intention of promoting wider, safe therapeutic application of NAM.

KEY SCIENTIFIC CONCEPTS OF REVIEW

NAM, by itself or through altering metabolic balance of NAD⁺ and tryptophan, modulates mitochondrial function and activities of many molecules and thereby positively affects cell viability and metabolic functions. And, NAM administration appears to be quite safe with limited possibility of side effects which are related to NAM's metabolites.

Programmed necrotic cell death of macrophages: Focus on pyroptosis, necroptosis, and parthanatos

Macrophages are highly plastic cells of the innate immune system. Macrophages play central roles in immunity against microbes and contribute to a wide array of pathologies. The processes of macrophage activation and their functions have attracted considerable attention from life scientists. Although macrophages are highly resistant to many toxic stimuli, including oxidative stress, macrophage death has been reported in certain diseases, such as viral infections, tuberculosis, atherosclerotic plaque development, inflammation, and sepsis. While most studies on macrophage death focused on apoptosis, a significant body of data indicates that programmed necrotic cell death forms may be equally important modes of macrophage death. Three such regulated necrotic cell death modalities in macrophages contribute to different pathologies, including necroptosis, pyroptosis, and parthanatos. Various reactive oxygen and nitrogen species, such as superoxide, hydrogen peroxide, and peroxynitrite have been shown to act as triggers, mediators, or modulators in regulated necrotic cell death pathways. Here we discuss recent advances in necroptosis, pyroptosis, and parthanatos, with a strong focus on the role of redox homeostasis in the regulation of these events.

[Extraction and purification of NUDT9 homology domain of human transient receptor potential melastatin 2 channel]

OBJECTIVE

To develop methods of extraction and purification of Cterminal NUDT9 homology domain of human transient receptor potential melastatin 2 (TRPM2) channel.

METHODS

After sonication and centrifuge of Escherichia coli strain Rosetta (DE3) which was induced by isopropylthio-β-D-galactoside, GST-NUDT9-H was collected after the binding of supernatant with GST beads and eluted with reduced glutathione. Then the elution buffer containing fusion protein was purified by size exclusion chromatography after concentration and centrifuge. Finally, with the cleavage of thrombin and binding with the GST beads, NUDT9-H with high purity in supernatant was collected.

RESULTS

The GST-NUDT9-H fusion protein was stabilized with lysis buffer containing 0.5% n-dodecyl -β-d-maltoside (DDM), and wash buffer containing 0.025% DDM in size-exclusion chromatography system, and finally the NUDT9-H with high purity was obtained after cleaved by thrombin (1 U/2 mg fusion protein) for 24 h.

CONCLUSIONS

Due to the poor stability of NUDT9-H, it is necessary to add DDM in extraction and purification buffer to stabilize the conformation of NUDT9-H, so as to increase its yields and purity.

Sedoheptulose-1,7-bisphospate Accumulation and Metabolic Anomalies in Hepatoma Cells Exposed to Oxidative Stress

We have previously shown that GSH depletion alters global metabolism of cells. In the present study, we applied a metabolomic approach for studying the early changes in metabolism in hydrogen peroxide- (H₂O₂-) treated hepatoma cells which were destined to die. Levels of fructose 1,6-bisphosphate and an unusual metabolite, sedoheptulose 1,7-bisphosphate (S-1,7-BP), were elevated in hepatoma Hep G2 cells. Deficiency in G6PD activity significantly reduced S-1,7-BP formation, suggesting that S-1,7-BP is formed in the pentose phosphate pathway as a response to oxidative stress. Additionally, H₂O₂ treatment significantly increased the level of nicotinamide adenine dinucleotide phosphate (NADP⁺) and reduced the levels of ATP and NAD⁺. Severe depletion of ATP and NAD⁺ in H₂O₂-treated Hep G2 cells was associated with cell death. Inhibition of PARP-mediated NAD⁺ depletion partially protected cells from death. Comparison of metabolite profiles of G6PD-deficient cells and their normal counterparts revealed that changes in GSH and GSSG per se do not cause cell death. These findings suggest that the failure of hepatoma cells to maintain energy metabolism in the midst of oxidative stress may cause cell death.

Genipin protects against H2O2-induced oxidative damage in retinal pigment epithelial cells by promoting Nrf2 signaling

Oxidative stress serves a vital function in the pathogenesis of age-related macular degeneration (AMD); genipin (GP) possesses antioxidative properties. The present study aimed to investigate the effects of GP on retinal pigment epithelial (RPE) cells induced by H₂O₂ and the underlying mechanism. ARPE-19 cells were subjected to H₂O₂ treatment to induce oxidative damage. Cell viability was determined via an MTT assay. Reactive oxygen species (ROS) levels and cell apoptosis were detected by flow cytometry. Nuclear factor-erythroid 2-related factor-2 (Nrf2) signaling-associated and the expression of apoptosis-associated factors were measured using reverse transcription-quantitative polymerase chain reaction assay and western blotting. The results revealed that 200 µM H₂O₂ and 30 µM GP were determined to be the optimal concentrations for subsequent experimentation. GP reversed the inhibitory effects of H₂O₂ by promoting cell viability, attenuating ROS accumulation and cell apoptosis, and increased the expression of Nrf2, heme oxygenase-1 (HO-1) and NAD(P)H: Quinine oxidoreductase 1 (NQO1); Nrf2 silencing inhibited HO-1 and NQO1 expression. In addition, Nrf2 silencing enhanced the effects of H₂O₂ by promoting ROS production and cell apoptosis. Compared with H₂O₂, Nrf2 silencing further decreased the expression levels of B-cell lymphoma-2 (Bcl-2), but increased that of Bcl-2-associated X protein and cleaved-caspase-3. The results of the present study revealed that Nrf2 silencing attenuated the protective effects of GP on H₂O₂-induced injury in ARPE-19 cells by promoting apoptosis and oxidation. Collectively, GP attenuated oxidative damage induced by H₂O₂ in ARPE-19 cells. Furthermore, the molecular mechanism may be associated with the Nrf2 signaling pathway. The findings of the present study nay provide insight into a potential therapeutic agent for the treatment of AMD.

Nicotinamide reverses behavioral impairments and provides neuroprotection in 3-nitropropionic acid induced animal model ofHuntington's disease: implication of oxidative stress- poly(ADP- ribose) polymerase pathway

Huntington's disease (HD) is characterized by cognitive and psychiatric impairment caused by neuronal degeneration in the brain. Several studies have supported the hypothesis that oxidative stress is the main pathogenic factor in HD. The current study aims to determine the possible neuroprotective effects of nicotinamide on 3-nitropropionic acid (3-NP) induced HD. Male Wistar albino rats were divided into six groups. Group I was the vehicle-treated control, group II received 3-NP (20 mg/kg, intraperitoneally (i.p.) for 4 days, group III received nicotinamide (500 mg/kg, i.p.). The remaining groups received a combination of 3-NP plus nicotinamide 100, 300 or 500 mg/kg, i.p. respectively for 8 days. Afterward, the motor function and hind paw activity in the limb withdrawal were tested; rats were then euthanized for biochemical and histopathological analyses. Treatment of rats with 3-NP altered the motor function, elevated oxidative stress and caused significant histopathological changes in the brain. The treatment of rats with nicotinamide (100, 300 and 500 mg/kg) improved the motor function tested by locomotor activity test, movement analysis, and limb withdrawal test, which was associated with decreased oxidative stress markers (malondialdehyde, nitrites) and increased antioxidant enzyme (glutathione) levels. In addition, nicotinamide treatment decreased lactate dehydrogenase and prevented neuronal death in the striatal region. Our study, therefore, concludes that antioxidant drugs like nicotinamide might slow progression of clinical HD and may improve the motor functions in HD patients. To the best of our knowledge, this study is the first to explore the neuroprotective effects of nicotinamide on 3-NP-induced HD.

NAD metabolism: Implications in aging and longevity

Nicotinamide adenine dinucleotide (NAD) is an important co-factor involved in numerous physiological processes, including metabolism, post-translational protein modification, and DNA repair. In living organisms, a careful balance between NAD production and degradation serves to regulate NAD levels. Recently, a number of studies have demonstrated that NAD levels decrease with age, and the deterioration of NAD metabolism promotes several aging-associated diseases, including metabolic and neurodegenerative diseases and various cancers. Conversely, the upregulation of NAD metabolism, including dietary supplementation with NAD precursors, has been shown to prevent the decline of NAD and exhibits beneficial effects against aging and aging-associated diseases. In addition, many studies have demonstrated that genetic and/or nutritional activation of NAD metabolism can extend the lifespan of diverse organisms. Collectively, it is clear that NAD metabolism plays important roles in aging and longevity. In this review, we summarize the basic functions of the enzymes involved in NAD synthesis and degradation, as well as the outcomes of their dysregulation in various aging processes. In addition, a particular focus is given on the role of NAD metabolism in the longevity of various organisms, with a discussion of the remaining obstacles in this research field.

Hydrogen Sulfide Protects Human Cardiac Fibroblasts Against H2O2-induced Injury Through Regulating Autophagy-Related Proteins

Autophagy, an intracellular bulk degradation process of proteins and organelles, can be induced by myocardial ischemia in the heart. However, the causative role of autophagy in the survival of human cardiac fibroblasts and the underlying mechanisms are incompletely understood. Oxidative stress can induce autophagy in cultured cells upon hydrogen peroxide (H₂O₂) exposure. Because hydrogen sulfide (H₂S) regulates reactive oxygen species (ROS) and apoptosis, we hypothesize that H₂S may have a cardioprotective function. To examine our hypothesis, we investigated the regulation of autophagy by the H₂S donor sodium hydrosulfide (NaHS), using a cell model of human cardiac fibroblasts from adult ventricles (HCF-av) that suffered from endoplasmic reticulum (ER) stress by H₂O₂. In the present study, we found that the apoptosis and autophagy were induced along with ER stress by H₂O₂ in the primary cultured HCF-av cells. In contrast, H₂S suppressed HCF-av cell apoptosis and autophagic flux, in part directly by inhibiting ROS production and preserving mitochondrial functions.

Over-expression of CNTF in bone marrow mesenchymal stem cells protects RPE cells from short-wavelength, blue-light injury

Increasing evidence has demonstrated that excessive blue-light (BL) with high photochemical energy and phototoxicity could induce apoptosis in retinal pigment epithelium (RPE) cells. RPE apoptosis leads to retina damage and further aggravate age-related macular degeneration (ARMD). Because of their neuroprotective, plasticity, and immunomodulatory ability, bone marrow mesenchymal stem cells (BMSCs) are recognized for retinal neuroprotection. RPE cells possess ciliary neurotrophic factor (CNTF) receptor complexes and can respond to CNTF; hence, we investigated the effects of BMSCs over-expressing CNTF on BL-injured RPE cells. BL-injured RPE cells were co-cultured with CNTF-BMSCs and GFP-BMSCs for 24 and 48 h. Superoxide dismutase and malondialdehyde assays were conducted to examine the effects of CNTF-BMSCs on the oxidative stress of RPE cells. VEGF protein secretion by RPE was determined by ELISA, and western blotting analysis was used to determine apoptotic protein expression and autophagic flux. Immunofluorescence was used to demonstrate the relationship between autophagy and apoptosis. We found that CNTF-BMSCs enhanced antioxidant capacity, decreased VEGF secretion, promoted autophagic flux, and inhibited apoptosis in BL-injured RPE cells, compared to GFP-BMSCs. Our findings suggest that CNTF over-expression enhances the protective effects of BMSCs on RPE cells, thus indicating subretinal-transplantation of CNTF-BMSCs may be a promising therapy for BL-injured retina.

Mitochondria-targeted ubiquinone (MitoQ) enhances acetaldehyde clearance by reversing alcohol-induced posttranslational modification of aldehyde dehydrogenase 2: A molecular mechanism of protection against alcoholic liver disease

Alcohol metabolism in the liver generates highly toxic acetaldehyde. Breakdown of acetaldehyde by aldehyde dehydrogenase 2 (ALDH2) in the mitochondria consumes NAD⁺ and generates reactive oxygen/nitrogen species, which represents a fundamental mechanism in the pathogenesis of alcoholic liver disease (ALD). A mitochondria-targeted lipophilic ubiquinone (MitoQ) has been shown to confer greater protection against oxidative damage in the mitochondria compared to untargeted antioxidants. The present study aimed to investigate if MitoQ could preserve mitochondrial ALDH2 activity and speed up acetaldehyde clearance, thereby protects against ALD. Male C57BL/6 J mice were exposed to alcohol for 8 weeks with MitoQ supplementation (5 mg/kg/d) for the last 4 weeks. MitoQ ameliorated alcohol-induced oxidative/nitrosative stress and glutathione deficiency. It also reversed alcohol-reduced hepatic ALDH activity and accelerated acetaldehyde clearance through modulating ALDH2 cysteine S-nitrosylation, tyrosine nitration and 4-hydroxynonenol adducts formation. MitoQ ameliorated nitric oxide (NO) donor-mediated ADLH2 S-nitrosylation and nitration in Hepa-1c1c7 cells under glutathion depletion condition. In addition, alcohol-increased circulating acetaldehyde levels were accompanied by reduced intestinal ALDH activity and impaired intestinal barrier. In accordance, MitoQ reversed alcohol-increased plasma endotoxin levels and hepatic toll-like receptor 4 (TLR4)-NF-κB signaling along with subsequent inhibition of inflammatory cell infiltration. MitoQ also reversed alcohol-induced hepatic lipid accumulation through enhancing fatty acid β-oxidation. Alcohol-induced ER stress and apoptotic cell death signaling were reversed by MitoQ. This study demonstrated that speeding up acetaldehyde clearance by preserving ALDH2 activity critically mediates the beneficial effect of MitoQ on alcohol-induced pathogenesis at the gut-liver axis.

•

PTMs of ALDH2 participated in the pathogenesis of alcoholic liver disease.

•

MitoQ treatment accelerated acetaldehyde detoxification.

•

MitoQ ameliorated acetaldehyde-related tight junction disruption.

•

MitoQ reversed TLR4-mediated inflammatory response in alcoholic liver disease.

•

MitoQ counteracts alcohol-induced ER stress and cell apoptosis.

Cellular Senescence in Age-Related Macular Degeneration: Can Autophagy and DNA Damage Response Play a Role?

Age-related macular degeneration (AMD) is the main reason of blindness in developed countries. Aging is the main AMD risk factor. Oxidative stress, inflammation and some genetic factors play a role in AMD pathogenesis. AMD is associated with the degradation of retinal pigment epithelium (RPE) cells, photoreceptors, and choriocapillaris. Lost RPE cells in the central retina can be replaced by their peripheral counterparts. However, if they are senescent, degenerated regions in the macula cannot be regenerated. Oxidative stress, a main factor of AMD pathogenesis, can induce DNA damage response (DDR), autophagy, and cell senescence. Moreover, cell senescence is involved in the pathogenesis of many age-related diseases. Cell senescence is the state of permanent cellular division arrest and concerns only mitotic cells. RPE cells, although quiescent in the retina, can proliferate in vitro. They can also undergo oxidative stress-induced senescence. Therefore, cellular senescence can be considered as an important molecular pathway of AMD pathology, resulting in an inability of the macula to regenerate after degeneration of RPE cells caused by a factor inducing DDR and autophagy. It is too early to speculate about the role of the mutual interplay between cell senescence, autophagy, and DDR, but this subject is worth further studies.

Poly(ADP-ribose)polymerases inhibitors prevent early mitochondrial fragmentation and hepatocyte cell death induced by H2O2

Poly(ADP-ribose)polymerases (PARPs) are a family of NAD⁺ consuming enzymes that play a crucial role in many cellular processes, most clearly in maintaining genome integrity. Here, we present an extensive analysis of the alteration of mitochondrial morphology and the relationship to PARPs activity after oxidative stress using an in vitro model of human hepatic cells. The following outcomes were observed: reactive oxygen species (ROS) induced by oxidative treatment quickly stimulated PARPs activation, promoted changes in mitochondrial morphology associated with early mitochondrial fragmentation and energy dysfunction and finally triggered apoptotic cell death. Pharmacological treatment with specific PARP-1 (the major NAD⁺ consuming poly(ADP-ribose)polymerases) and PARP-1/PARP-2 inhibitors after the oxidant insult recovered normal mitochondrial morphology and, hence, increased the viability of human hepatic cells. As the PARP-1 and PARP-1/PARP-2 inhibitors achieved similar outcomes, we conclude that most of the PARPs effects were due to PARP-1 activation. NAD⁺ supplementation had similar effects to those of the PARPs inhibitors. Therefore, PARPs activation and the subsequent NAD⁺ depletion are crucial events in decreased cell survival (and increased apoptosis) in hepatic cells subjected to oxidative stress. These results suggest that the alterations in mitochondrial morphology and function seem to be related to NAD⁺ depletion, and show for the first time that PARPs inhibition abrogates mitochondrial fragmentation. In conclusion, the inhibition of PARPs may be a valuable therapeutic approach for treating liver diseases, by reducing the cell death associated with oxidative stress.

RNA-Seq Analysis of the Antioxidant Status and Immune Response of Portunus trituberculatus Following Aerial Exposure

Desiccation tolerance has been long considered as an important trait for the life survival under acute environmental stress. One of the biggest problems for modern commercial crab farming is desiccation during transportation; high mortality could occur following the aerial exposure. In this regard, here, we utilized RNA-seq-based transcriptome profiling to characterize the molecular responses of swimming crab in response to aerial exposure. In present study, following aerial exposure, the gill samples were sequenced at 0, 6, 12, and 18 h. And the sequenced reads were assembled into 274,594 contigs, with average length of 735.59 bp and N50 size of 1262 bp. After differential expression analysis, a total of 1572 genes were captured significantly differentially expressed, and were categorized into antioxidant/oxidative stress response, chaperones/heat shock proteins, immune alteration, cell proliferation/apoptosis, and cytoskeletal. Our analysis revealed the dramatic tissue oxidant stress and the alteration of the tissue epithelial integrity, especially many genes that have not been reported in crab species. With the limited functional information in crab, further studies are needed and underway in our lab to further characterize the key cellular actors governing the crab tolerance to aerial exposure. Taken together, our results provide molecular resources for further identification of key genes for desiccation tolerance, and to facilitate the molecular selection and breeding of desiccation tolerant strain and family.

Autophagy regulates death of retinal pigment epithelium cells in age-related macular degeneration

Age-related macular degeneration (AMD) is an eye disease underlined by the degradation of retinal pigment epithelium (RPE) cells, photoreceptors, and choriocapillares, but the exact mechanism of cell death in AMD is not completely clear. This mechanism is important for prevention of and therapeutic intervention in AMD, which is a hardly curable disease. Present reports suggest that both apoptosis and pyroptosis (cell death dependent on caspase-1) as well as necroptosis (regulated necrosis dependent on the proteins RIPK3 and MLKL, caspase-independent) can be involved in the AMD-related death of RPE cells. Autophagy, a cellular clearing system, plays an important role in AMD pathogenesis, and this role is closely associated with the activation of the NLRP3 inflammasome, a central event for advanced AMD. Autophagy can play a role in apoptosis, pyroptosis, and necroptosis, but its contribution to AMD-specific cell death is not completely clear. Autophagy can be involved in the regulation of proteins important for cellular antioxidative defense, including Nrf2, which can interact with p62/SQSTM, a protein essential for autophagy. As oxidative stress is implicated in AMD pathogenesis, autophagy can contribute to this disease by deregulation of cellular defense against the stress. However, these and other interactions do not explain the mechanisms of RPE cell death in AMD. In this review, we present basic mechanisms of autophagy and its involvement in AMD pathogenesis and try to show a regulatory role of autophagy in RPE cell death. This can result in considering the genes and proteins of autophagy as molecular targets in AMD prevention and therapy.